1. Field of the Invention
The present invention relates to a telephone answering device having remote controlled message playback capability.
2. Description of the Prior Art
Telephone answering devices have gained widespread acceptance for both home and office use. With such a device, no call goes unanswered, even when the user is away from his home or office.
A particularly useful feature of some answering devices is the ability of the user to have his messages played out automatically by remote control. Typically, when the user is away from his home or office and desires to hear his messages, he will call his own telephone number. When the device answers the telephone automatically, the user will transmit a beep tone via the telephone which will cause the answering device to switch into a remote playout mode. The tape containing the recorded incoming messages is quickly rewound, and then set to the forward direction to play back the recorded messages via the telephone line. When all of the messages have been played out, the device stop and reverts back to the answering mode.
In the past, such remote playout capability has necessitated complex mechanical and electronic arrangements, thereby considerably increasing the cost of the answering device. This increased cost often took the device out of the price range of the ordinary household user. A principal object of the present invention is to provide a telephone answering device having remote playout capability while using simple, inexpensive electronic and mechanical components.
Certain minimal functions must be achieved to accomplish remote playout. First, circuitry must be provided to detect the beep tone and to switch the device from the automatic answering mode to the remote playout mode in response to such detection. An electromechanical arrangement then must be provided first to rewind the tape on which the incoming messages have been recorded and then to drive the tape in the forward direction as the messages are played out over the telephone line to the user. A further mechanism must be provided to terminate the remote playout operation and to transfer the device back to the automatic answering mode when remote playout has been completed. Optionally, the device also may be configured to allow rewinding of the message tape after the recorded messages have been played out so that the full supply of tape is available to record subsequent incoming messages.
One approach of the prior art is typified by the apparatus shown in U.S. Pat. No. 3,067,289 to Zimmermann. There, as the incoming messages are recorded an integrating timer, mechanically coupled to the recorder, provides an index of the total elapsed recording time. When the tape is rewound in response to receipt of a remote control signal, the integrating timer retains its prior position. Then, as the recorded messages are played out to the user a cam is mechanically advanced. When the message playout time equals the elapsed recording time stored by the integrating timer, the cam closes a microswitch to terminate the playout operation.
In the prior art system just described, a complex mechanical arrangement is required to function as the integrating timer. Other prior art devices utilize different types of mechanical timers to control the playout duration of the recorded messages. An alternative approach, not requiring an integrating timer, is to have the user terminate the playout cycle after he has heard all of the messages. This is accomplished by having the user send a second beep control signal over the telephone line. This is detected by the device and used to terminate the playout operation. Another object of the present invention is to provide an improved, low-cost telephone answering device of this type in which the remote playout operation is terminated upon receipt of a second beep tone from the user.
Another factor which has added to the cost of prior art telephone answering devices involves the circuitry for mode switching. During the automatic answering cycle, the device must be able to switch from the outgoing announcement transmit mode to the incoming message record mode. In prior art devices this has often necessitated the use of one or more relays or independent flip-flop circuits. A further object of the present invention is to provide a unique mode control flip-flop arrangement in which the audio amplifiers used to amplify outgoing and incoming speech also are used as components of a mode control flip-flop, thereby eliminating the need for a separate flip-flop circuit.
Prior art devices also have employed relays or separate flip-flop circuits for motor drive control and for switching between the automatic answering and the remote playout modes. Another object of the present invention is to provide simplified motor drive circuitry which requires no relay or flip-flop but which facilitates the alternative supply of power to the loop drive motor or the reel drive motor. Another object of the present invention is to provide a remote playout control flip-flop of unique circuitry employing only a single operational amplifier to perform a bistable switching function.
Another desirable feature of a telephone answering device is to have it powered from the commercial ac power line. This eliminates the cost and nuisance of battery replacement. However, as a result of the capacitive coupling in the ac power transformer, prior art ac powered answering device have had the shortcoming of presenting an unbalanced load to the telephone line. That is, one input terminal of the device may have presented a different capacitive impedance to ground to the telephone line than did the other input terminal. A further object of the present invention is to overcome this objectionable unbalanced load situation and to provide an ac powered answering device which presents a balanced load to the telephone line.